For this article a few tips on how you can use  a compressor to push your amp to create overdriven-and distorted sounds. Most of these ideas will work well with amps which do have a gain-and master volume stage. Amps which have only one volume control may not give you the same results, just try to see how your amps responds to the compressor.

Compressors can be used to sustain notes, to add a bit of brightness to your amp and to add more volume to your overall sound. Compressors are also able to excite the overdrive stage of your amp quicker, since they can add more volume to your guitar amp. Using a compressor in this manner may give you a more subtle kind of overdrive instead of the full-tilt overdrive you may get at the moment.
To achieve this sound, basically set your pre-amp (or gain) level just before it kicks in, your sound should still be clean when you play. Now set the compressor up to add more volume, adjust the amount of compression, you do not want too much compression as we are after volume instead of more compression.
Adding a Equalizer to the mix can bring out more treble and may make the sound more realistic. Be careful with how much you boost on the Equalizer, you only want a little bit more treble and maybe bass, depending on your amp. You may even want to put the Equalizer in the loop of your amp, leave the compressor at the front end of your amp, as it will work better at that end.

Compare the sound you are getting using the compressor to your regular kind of distorted (or overdriven) sound. At first you may not feel there is much difference, but it may be just because you may not be used to using the compressor in this way.

Good luck and hope to catch you soon again for more.
Eddie